In recent years, studies have been conducted on constructing a model of the intake system of an internal combustion engine based on fluid dynamics etc. and using that model to calculate parameters to control the internal combustion engine. That is, for example, a throttle model, intake pipe model, intake valve model, etc. have been constructed for the intake system of internal combustion engines, these models have been used to calculate the cylinder filling air amount etc. from the throttle valve opening degree, atmospheric pressure, atmospheric temperature, etc. and these have been used to control internal combustion engines.
However, when controlling an internal combustion engine, in particular when using the above model to control an internal combustion engine, to calculate the parameters related to the control, sometimes the throttle valve downstream side intake pipe pressure Pmta or cylinder intake air flow mcta at the time of steady operation (or the cylinder air filling rate Klta at the time of steady operation obtained calculated from that (that is, the ratio of mass of cylinder filling air with respect to the mass of the air of the total stroke capacity of the cylinder)) becomes necessary. For example, Japanese Patent Publication (A) No. 2001-41095 discloses a method of calculating a throttle valve passage air flow based on the throttle valve downstream side intake pipe pressure, atmospheric pressure, etc. at that time and the Pmta.
Further, the above throttle valve downstream side intake pipe pressure Pmta or cylinder intake air flow mcta at the time of steady operation has conventionally been found using a map. That is, for example, in the Japanese Patent Publication (A) No. 2001-41095, the Pmta is found from a map using the throttle valve opening degree and/or engine speed etc. as arguments.
However, when actually preparing such a map, a tremendous amount of time becomes necessary. That is, to prepare a map, it is necessary to actually measure the Pmta or mcta while successively changing the arguments. This work becomes tremendous. Further, there is the concern that an increase in the necessary maps or arguments will increase the map searching operation and increase the control load.